The Optimization Of Vertical Constructed Wetlands And Its Microbial Diversity Analysis

Constructed wetlands (CWs) are cost-effective, simple, low energy cost and natural technology for water treatment, which have received considerable attention during recent years. However, the traditional CWs are mainly reconstructed through the original wetland which restricted their development. Ambient temperature affects the microbial activity and then the CWs’treatment efficiency. To mitigate the negative effect of low temperature, we optimized the CWs conditions and studied their stability. Also, the microbial diversity was analyzed to investigate its relationship with pollutants removal. Additionally, CH4 flux could mitigate the environmental benefits of nutrients removal in these man-made ecosystems. So, we detected the CH4 fluxes and analyzed the microbial mechanisms, which provide theoretical and experimental basis for the CWs optimization and environmental protection. The main results are summarized as follows:(1) Several microcosms were constructed to detect the effects of monoculture and mixture planted system on the pollutants removal, CH4 flux and microbial community diversity. Plant species richness enhanced the pollutants removal but the higher CH4 flux mitigated the environmental benefits. Qualitative and quantitative analysis of the methanogens and methanotrophs diversity exhibited a relative stability for the microbial community structures, but the populations varied. The relatively higher methanogens and the lowest methanotrophs might be the main reason that resulted in the higher methane flux in the mixture system. Rumex japonicus performed better than other plant species in mediating nitrogen removal and may play an important role in the mixture CWs.(2) In the Integrated Vertical Constructed Wetlands (IVCWs), increased hydraulic loading (HL) (0.2,0.4,0.8 and 1.6 m·d-1) decreased the NH4+-N removal (88%,87%,83% and 76%), but slightly influenced the NO3--N and CODMn removal. The organic pollutants in the present study were mainly removed by anaerobic degradation because of the low DO concentration in the influent. A higher CH4 flux was founded in the higher HL system.0.8 m·d-1 will be a proper hydraulic loading rate for the pollutants removal and environmental benefits.The dominant bacteria were different between Down-flow and Up-flow, but showed no significant difference among studied HL. Nitrosomonas and Nitrospira were the main ammonia oxidation bacteria (AOB) and nitrite oxidation bacteria (NOB) in different system and showed a higher diversity in the Up-flow unit. The relative abundance of amoA gene was higher in the Down-flow unit and decreased with HL increasing. Denitrifying bacteria diversity was high and more vulnerable to HL. The relative abundance of nirS gene was higher than that of amoA gene. And the high HL (1.6 m·d-1) system had the highest nirS gene abundance which represented the high denitrifying bacteria abundance and revealed the high NO3--N removal.Qualitative and quantitative analysis of the methanogens and methanotrophs diversity revealed that the relative abundance of methanogens increased with the increasing HL, but the methanotrophs abundance was only different between the high (1.6 m·d-1) and low (0.2 m·d-1) system. Methanogens were vulnerable to HL. The phylogenic analysis showed a high diversity of methanogens and most of the clones were classified into Methanomicrobiales; methanotrophic diversity was low and showed less difference among different HLs. Methylocystaceae was the main methanotrophs in the study.(3) IVCW exhibited a high (about 80%)and stable NH4+-N removal performance, but the NO3--N removal was sensitive to ambient temperature changes. CODMn removal was relatively stable in the temperature ranging between -4 and 39℃ because of the low concentration of organic matters in the influent. Clone library analysis of amoA gene showed a relative stable AOB diversity in the system during the running period which was favorable to the NH4+-N removal stability. AOB dominated over NOB. The abundance and diversity of denitrifying bacteria changed with the temperature variation. Low temperature decreased the relative abundance of denitrifying bacteria and then the NO3--N removal.